Phosphinate species are typically difficult to prepare especially when the substituent group is unsaturated. The unsaturated species reported are typically alkenes with some rare examples of allenes. In any case, such species are difficult to prepare and typically require either multi-steps preparation or catalysis. In addition, the species generated such as the alkene phosphinates only have a limited reactivity in polymerization. As far as we know, no 1,3-diene phosphinate has been reported in the literature whereas such structure could have some very interesting reactivity.
The closest structures reported are 1,2-diene (aka allenes) such as in Russian papers (Antibiot. Ferm. Med. Naznachen., Leningrad, USSR. Doklady Akademii Nauk SSSR (1983), 269(6), 1377-80 OR Belakhov, V. V.; and al., Zhurnal Obshchei Khimii (1983), 53(7)). These allenes structures are synthesized from acetylenic alcohols and hypophosphorous acids.
In the literature the reactivity of α,β-unsaturated carbonyl compounds has been widely studied and Mauser (Chem. Rev., 1963, 63 (3), pp 311-324) specifically studied the reactivity of mesityl oxide. Typically such compounds can either react at the carbonyl or at the double bond. Usually, the reaction at the carbonyl with strong nucleophilic compounds such as Grignard reagents afford the corresponding hydroxyl adducts or the allenes (1,2-dienes) if the dehydration takes place. When the reactions take place at the double bond with other nucleophilic compounds such as amines or alcohols the mechanism is a 1,4 addition leading to the formation of the corresponding ketone. In particular the reaction of mesityl oxide with dialkylphosphites lead selectively to the formation of the ketones.
There are different types of inimers. For example, U.S. Pat. No. 6,156,859 described a cationic inimer to create hyperbranched iso-olefins U.S. application 2006-849415P uses halogenated inimers to make hyperbrached polymers by self-condensing vinyl ATRP (Atomic Transfer Radical Polymerization). However, the radical inimers, which is not easy to prepare, are halogenated compounds and metal co-initiator is required. Halogens are considered toxic and the use of metal often contaminates the polymers.
There is an increasing need for more efficient inimers, i.e., monomeric initiators, capable of creating hyperbranched polymer structures via different mechanisms (radical, catalytic etc . . . ). A H-phoshinate diene would provide a unique structure capable of playing such a role.
Today, metallic phosphinates is the leading technology to replace halogenated flame retardants. However, the main process to prepare this family of compounds is difficult and overall expensive. There is a real need to develop a new cost efficient chemistry allowing preparation of phosphinate or polymeric phosphinate that could be used as flame retardants.
The leading chemistry to prepare dialkylphosphinate salts for use in flame retardants is based on Clariant chemistry (U.S. Pat. No. 6,329,544) which consists in reacting olefins with hypophosphorous acid under very harsh conditions. In particular the reaction of ethylene and hypophosphorous acid is widely used to prepare well known flame retardants. Another chemistry widely used as flame retardant is the DOPO that is a cyclic H-phosphinate and its chemistry is based on PCl3. This chemistry is not ideal when trying to prepare halogen free flame retardants.
Phosphinate compounds are well known to be widely used in the mining industry to separate metals. There are some attempts to fix them on polymeric structures to enable to have solid supported extractants. However, this strategy is somehow expensive due to the difficulty to graft durably phosphinate groups on polymeric structures. H-phosphinate diene structures if they were available could allow designing some new polymeric structure having a high density of phosphinic groups thus allowing a good metallic separation.